Relays and switches are used in a variety of industrial and commercial applications where there is a need to control power. A relay may be either an electromechanical or solid-state device to control other devices connected to an output. Relays are generally associated with controlling the transmission of electric current in a circuit.
Electromechanical relays are used as switches that make or break a circuit by mechanical operation. Here, an electromagnet moves an armature when current flows through the electromagnet, and the armature acts as a switch. Where the magnetic field produced by a current-carrying coil is used to magnetize and move a plunger, the electromagnet may also be referred to as a solenoid.
It is known to employ either electromechanical or solid-state switches in order to ensure proper polarity connection between two sources of power. One exemplary application for such use is in the automotive field for the purpose of interconnecting rechargeable batteries. It is not uncommon for vehicles having rechargeable batteries, such as automobiles, busses, trucks, etc. and even watercraft to require boosts on their batteries from external sources of DC power. For example, in emergency situations, it may be necessary to jump-start a vehicle by connecting one vehicle's “dead” battery to another vehicle's “live” battery. Jumper cables can be used for this purpose, but it is imperative to connect the batteries with proper polarity, i.e. positive to positive and negative to negative. Failure to do so can potentially cause serious damage to either or both vehicles' electrical systems.
In the past, a variety of techniques have been employed by others to ensure proper interconnection between vehicle batteries. For example, U.S. Pat. No. 4,400,658 to Yates, issued Aug. 23, 1983, relates to a battery cable jumper arrangement incorporating a plurality of solenoids and a switching arrangement. A pair of double pole, double throw (DPDT) switches are actuated by the solenoids to ensure correct polarity of connection between the power source and the battery, irrespective of the connected arrangement of the cable pairs. In U.S. Pat. No. 5,103,155 to Joannou, issued Apr. 7, 1992, a battery charging system utilizes solid-state components interconnected between two pairs of booster cables. Joannou's device incorporates an electronic polarity sensing, monitoring and alarm circuit and a polarity sensing relay.